The present invention relates to a method of producing fine particles by a sputtering process and more particularly to a method of producing fine particles with a crystalline or amorphous structure in a high yield using a pretreated substrate.
In recent years, it has been found that fine particles with a particle size of submicron or smaller have useful properties, for example, a considerable increase in specific surface area, a lowering in melting point, a significant increase in surface activity, magnetically single domain, etc., which are different from the properties inherent in larger particles. Accordingly, such fine particles have been greatly expected as new industrial materials and many studies have been extensively made on the production of the particles and their properties. As a method of producing such fine particles, there has been well known a method involving heating metals or alloys and vaporizing in an inert gas, such as argon, helium, etc., under reduced pressure, and the method has now been industrialized. Further, recently, as a technique for the mass production of the fine metal particles, there has been developed a method utilizing the reaction between activated hydrogen and molten metal and much attention is paid to the new method. However, the two methods set forth above are based on vaporizing phenomenon or the like and, thus, are unsuitable for producing fine particles from alloys or compounds comprising a few elements each having a different vapor pressure.
Recently, the sputtering phenomenon has been practically applied to thin film formation (sputtering method) and the method is widely utilized as a new industrial technique. When considered from the viewpoint of thin film formation, this new technique has the following advantageous aspects. The method is applicable even to elements or compounds with a high melting point and a low vapor pressure, which are not usable or present many difficulties in film formation by vacuum evaporating. Although film formation by sputtering is slow as compared with the vacuum evaporation method, it can readily produce a uniform thin film with a high reproducibility without causing a substantial deviation in composition. Further, the film formed by sputtering strongly adheres to the substrate. This strong adhesion is greatly advantageous for film formation, but, when considered from the viewpoint of the production of fine particles, this property is considerably unfavorable and thus it has been considered that the sputtering technique can not be utilized for producing fine particles.
In view of the above, the inventors of the present invention carried out extensive studies, particularly on the production of fine particles by the sputtering method from among various physical vapor-phase deposition methods and arrived at a novel production method described hereinafter.